|Publication number||US7542738 B2|
|Application number||US 11/314,228|
|Publication date||Jun 2, 2009|
|Filing date||Dec 21, 2005|
|Priority date||Dec 21, 2005|
|Also published as||US20070142003|
|Publication number||11314228, 314228, US 7542738 B2, US 7542738B2, US-B2-7542738, US7542738 B2, US7542738B2|
|Original Assignee||Intel Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (17), Referenced by (6), Classifications (14), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The invention relates generally to power amplifiers and, more particularly, to techniques for measuring and compensating for distortion and non-linearity in power amplifiers.
Many electronic applications have a need for linear power amplifiers. In the past, power amplifier linearity was often achieved by performing a factory calibration procedure to develop pre-emphasis compensation for the power amplifier to linearize the gain thereof. The compensation information would then be stored within the device carrying the power amplifier for use throughout the life of the amplifier. This factory calibration procedure can be complex and costly to perform for each item in a production line. In addition, this calibration technique only compensates for distortion in the power amplifier under the conditions that exist at the time the calibration is performed and does not provide compensation for effects such as gain variation as a function of junction temperature, gain variation as a function of component aging, non-linearity effects associated with the use of different modulation techniques, and/or other gain variations that might occur during component operation. There is a need for power amplifier linearization techniques that are capable of adapting to changing conditions associated with an amplifier.
In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the spirit and scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout the several views.
As will be described in greater detail, the low frequency AM modulation generator 26 generates a low frequency AM modulation signal that may be used to further modulate the carrier in a manner that allows the input-output characteristic of the PA 30 to be estimated. This low frequency AM modulation may then be removed from the RF signal after amplification but before the RF signal is output by the power amplification system 20. In at least one embodiment, the low frequency AM modulation signal is a sinusoid, although other signal types may alternatively be used (e.g., square wave, etc.). The LPF and RF block 28 is used to prevent higher frequencies generated by the low frequency AM modulation generator 26 (e.g., harmonics, etc.) from reaching the PA 30 and also to block RF frequencies in the modulated RF signal from reaching the generator 26. The filtered low frequency AM modulation signal may be delivered to the second modulator 29 to modulate the input signal before it is applied to the PA 30.
The PA 30 amplifies the input signal to generate an amplified output signal. The RF envelope detector 32 and the average RF power meter 34 measure features of the amplified output signal for use in a feedback loop designed to compensate for non-linearities in the power amplification system 20. The features that are measured are ones that allow an input-output characteristic of the PA 30 to be generated. It should be appreciated that other techniques for measuring features of the amplified output signal of the PA (i.e., other than envelope detection and average RF power measurement) from which an input-output characteristic can be developed may alternatively be used. The measured features (or information derived therefrom) may be delivered to the feedback controller 36 for use in generating an input-output characteristic for the PA 30. The feedback controller 36 may then use the estimated characteristic to develop compensation values for use in compensating for nonlinearities of the PA 30. The compensation values may be delivered to the RF signal modulation generator 22 for use in generating the RF modulation signal that will be used to modulate the RF carrier. The RF signal modulation generator 22 may use the compensation values received from the feedback controller 36 to provide pre-emphasis within the modulation signal in a manner that will reduce non-linearity in the system.
The HPF 38 is operative for high pass filtering the amplified output signal of the PA 30 to remove low frequency components resulting from the low frequency modulation associated with the modulation generator 26. The output of the HPF 38 is a linearly amplified version of a modulated RF signal that includes the data (or other information) originally input to the RF signal modulation generator 22. The output of the HPF 38 may then be delivered to an application specific destination. For example, when the power amplification system 20 is being used within a wireless communication application, the output of the HPF 38 may be delivered to an antenna to be transmitted to a remote wireless entity. Any type of antenna may be used including, for example, a dipole, a patch, a helical antenna, and/or others. In another application, the power amplification system 20 may be used within a wired communication network, in which case the output of the HPF 38 may be delivered to a wired network medium. Other power amplifier applications also exist.
The RF envelope detector 32 detects the envelope of the amplified signal output by the PA 30 and delivers information related to this envelope to the feedback controller 36. This information may include the full envelope, one or more portions of the envelope, information derived from the envelope, or other envelope-related information. The information may be digitized before being delivered to the feedback controller 36. The average power meter 34 measures the average RF power of the amplified signal output by the PA 30 and delivers this information to the feedback controller 36. As described previously, the feedback controller 36 may use the information received from the RF envelope detector 32 and the average power meter 34 to generate an input-output characteristic for the PA 30. The characteristic may then be used to develop compensation information. In at least one embodiment, the low frequency AM modulation applied by the low frequency AM modulation generator 26 is such that the modulation will not change the average power level of the signal modulated thereby (e.g., sinusoidal modulation, square wave modulation, etc.).
In one approach, the low frequency AM modulation generator 26 may provide dithering to the data modulated RF carrier to vary an amplitude of the signal between a high and a low value. The normal (non-dithered) amplitude of the data modulated RF carrier may be somewhere between the high and low amplitude values. When the signal including the dithering is applied to the PA 30, the PA 30 will amplify the high and low amplitude values differently based on the non-linear characteristic of the PA 30. The RF envelope detector 32 measures the envelope of the PA output signal. The feedback controller 36 or the envelope detector 32 can then read the amplitude of the envelope at portions of the PA output signal corresponding to the high and low amplitudes of the PA input signal. The feedback controller 36 can then use this information, in addition to the average power information, to generate input-output points of the input-output characteristic of the PA 30. The input-output characteristic may then be generated by the feedback controller 36 using, for example, a well known nonlinear regression algorithm or other curve fitting technique (e.g., a rolling average curve fit, etc.) to find a best fit curve for the measured points. The feedback controller 36 may be implemented using a digital processing device such as, for example, a general purpose microprocessor, a digital signal processor (DSP), a reduced instruction set computer (RISC), a complex instruction set computer (CISC), a microcontroller, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), and/or others, including combinations of the above. The digital processing device may be a dedicated unit (i.e., dedicated to feedback functions) or a unit that also performs other processing functions within the system.
When the signal 40 is applied to the PA, each of the dither levels 46, 48, 50, 52 will generate a corresponding PA output level based on the input-output characteristic of the PA. Each of these output levels may then be measured and recorded. Each output level and the corresponding input level will then form a dither state of the amplification system. Once a number of dither states have been collected, a regression algorithm may be used to develop a best fit curve for the dither states to generate the input-output characteristic of the amplification system.
After the RF carrier has been modulated, the signal may be applied to the input of a PA (block 96). The PA amplifies the modulated signal to generate an amplified output signal. Features of the amplified output signal are then measured to generate feedback information (block 98). As illustrated in
After the feedback information has been generated, the information may be used to generate an input-output characteristic of the PA (block 100). In at least one approach, nonlinear regression techniques may be used to generate a best fit curve for the collected feedback information. Other curve fitting techniques may alternatively be used. After the input-output characteristic has been generated, pre-emphasis compensation values or pre-emphasized waveforms may be generated based on the characteristic (block 102). That is, values or waveforms may be generated that indicate how much pre-emphasis needs to be used for various levels of a modulated input signal so that the PA output is relatively linear. Once the pre-emphasis information has been determined, it may be used to compensate for non-linearities in the system. This compensation may be performed using digital and/or analog techniques. In one possible approach, pre-emphasis compensation information, along with the input data to be amplified, are used in generating a subsequent modulation signal for the RF carrier.
After the PA generates the amplified output signal, all low frequency AM modulation components may be removed from the amplified signal before it proceeds to a system output (block 104). In one possible approach, a high pass filter is used to perform this function (see, e.g.,
The techniques and structures of the present invention may be implemented in any type of component, device, or system requiring linear power amplification. For example, features of the invention may be embodied within RF transmitters within: cellular telephones and other handheld wireless communicators; personal digital assistants having wireless capability; laptop, palmtop, desktop, and tablet computers having wireless capability; wireless network access points; base stations; pagers; RFID devices; satellite communicators; terrestrial wireless communicators; cameras having wireless capability; audio/video devices having wireless capability, network interface cards (NICs) and other network interface structures; RADAR systems; wired networking devices; integrated circuits; wireless networking chipsets; cellular chipsets; RFID chipsets; and/or other structures. Features of the invention may also be implemented as instructions and/or data structures stored on machine readable media, and/or in other formats. Examples of different types of machine readable media that may be used include floppy diskettes, hard disks, optical disks, compact disc read only memories (CD-ROMs), digital video disks (DVDs), Blu-Ray disks, magneto-optical disks, read only memories (ROMs), random access memories (RAMs), erasable programmable ROMs (EPROMs), electrically erasable programmable ROMs (EEPROMs), magnetic or optical cards, flash memory, and/or other types of media suitable for storing electronic instructions or data.
It should be appreciated that the individual blocks illustrated in the block diagrams herein may be functional in nature and do not necessarily correspond to discrete hardware elements. For example, in at least one embodiment, two or more of the blocks in a block diagram are implemented in software within a single (or multiple) digital processing device(s). The digital processing device(s) may include, for example, a general purpose microprocessor, a digital signal processor (DSP), a reduced instruction set computer (RISC), a complex instruction set computer (CISC), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), and/or others, including combinations of the above. Hardware, software, firmware, and hybrid implementations may be used.
In the foregoing detailed description, various features of the invention are grouped together in one or more individual embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects may lie in less than all features of each disclosed embodiment.
Although the present invention has been described in conjunction with certain embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US6438360 *||Jul 22, 1999||Aug 20, 2002||Motorola, Inc.||Amplifier system with load control to produce an amplitude envelope|
|US6529072 *||Sep 27, 2001||Mar 4, 2003||Hitachi Kokusai Electric Inc.||Predistortion-based amplifier, transmitter and envelope detector|
|US6606483 *||Oct 10, 2000||Aug 12, 2003||Motorola, Inc.||Dual open and closed loop linear transmitter|
|US6670849 *||Aug 30, 2000||Dec 30, 2003||Skyworks Solutions, Inc.||System for closed loop power control using a linear or a non-linear power amplifier|
|US6801784 *||Nov 2, 2000||Oct 5, 2004||Skyworks Solutions, Inc.||Continuous closed-loop power control system including modulation injection in a wireless transceiver power amplifier|
|US6836646 *||Mar 20, 2002||Dec 28, 2004||Samsung Electronics Co., Ltd||Circuit and method for compensating for non-linear distortion|
|US6898257 *||Feb 20, 2001||May 24, 2005||Lucent Technologies Inc.||Transmitter device having a modulation closed loop|
|US7068980 *||Oct 29, 2002||Jun 27, 2006||Electronics And Telecommunications Research Institute||Pre-distortion apparatus and method for recovering nonlinear distortion of high power amplifier|
|US7099636 *||Mar 18, 2003||Aug 29, 2006||Skyworks Solutions, Inc.||Continuous closed-loop power control system including modulation injection in a wireless transceiver power amplifier|
|US7218951 *||Jul 6, 2004||May 15, 2007||Skyworks Solutions, Inc.||Continuous closed-loop power control system including modulation injection in a wireless transceiver power amplifier|
|US7251464 *||Oct 4, 2004||Jul 31, 2007||Motorola, Inc.||Method and apparatus for predistortion training in an amplifier utilizing predistortion|
|US7277687 *||Dec 3, 2003||Oct 2, 2007||Starkey Laboratories, Inc.||Low power amplitude modulation detector|
|US7330518 *||Apr 16, 2004||Feb 12, 2008||Sony Ericsson Mobile Communications Japan, Inc.||Distortion compensation circuit, and a transmission apparatus including the same|
|US7369871 *||Aug 10, 2004||May 6, 2008||Skyworks Solutions, Inc.||System and method for allowing a TDMA/CDMA portable transceiver to operate with closed loop power control|
|US20080144709 *||Dec 19, 2006||Jun 19, 2008||Crestcom, Inc.||RF transmitter with predistortion and method therefor|
|US20080146168 *||Feb 8, 2005||Jun 19, 2008||Sige Semiconductor Inc.||Methods of Enhancing Power Amplifier Linearity|
|US20080285640 *||May 15, 2007||Nov 20, 2008||Crestcom, Inc.||RF Transmitter With Nonlinear Predistortion and Method Therefor|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8874397 *||Jan 14, 2011||Oct 28, 2014||National Instruments Corporation||User-invoked calibration of modular system using an embedded calibration signal generator|
|US9438357 *||Mar 5, 2015||Sep 6, 2016||Innovationszentrum Fuer Telekommunikationstechnik Gmbh Izt||Calibration device, signal processing device, and user interface for the same|
|US20090219088 *||Sep 28, 2006||Sep 3, 2009||Electronics And Telecommunications Research||Apparatus and method for correcting non-linear distortion based on characteristic modeling of high power amplifier|
|US20120185199 *||Jan 14, 2011||Jul 19, 2012||Moran Tamir E||User-Invoked Calibration of Modular System Using an Embedded Calibration Signal Generator|
|US20140257735 *||May 19, 2014||Sep 11, 2014||National Instruments Corporation||Calibration of modular system using an embedded calibration signal generator|
|US20150288463 *||Sep 5, 2013||Oct 8, 2015||Innovationszentrum für Telekommunikationstechnik GmbH IZT||Calibration device, signal processing device, and user interface for the same|
|U.S. Classification||455/114.3, 455/126, 455/115.1|
|International Classification||H03C1/62, H04B1/04|
|Cooperative Classification||H01Q9/04, H04B1/0475, H01Q9/16, H01Q1/362, H04B2001/0425|
|European Classification||H04B1/04L, H01Q1/36B, H01Q9/04, H01Q9/16|
|Dec 21, 2005||AS||Assignment|
Owner name: INTEL CORPORATION, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:POSAMENTIER, JOSHUA;REEL/FRAME:017407/0006
Effective date: 20051215
|Nov 21, 2012||FPAY||Fee payment|
Year of fee payment: 4
|Jan 13, 2017||REMI||Maintenance fee reminder mailed|
|Jun 2, 2017||LAPS||Lapse for failure to pay maintenance fees|
|Jul 25, 2017||FP||Expired due to failure to pay maintenance fee|
Effective date: 20170602